Endophyte in Perennial Grasses: Effect on Host Plants and Livestock
Note Number: AG0202
Paul Quigley and Kevin Reed, Hamilton
Updated: November, 1999
Endophytes are fungi that live within healthy plant tissue, relying on it for protection, nutrition and dispersal. Usually they do not cause any disease symptoms but can be detected by examining plant sections with a microscope or by laboratory tests.
There are many different strains of endophytes> Each is compatible with particular grass species or genotypes. Endophytes have been found in perennial ryegrass, annual ryegrass including L. multiflorum and L. rigidum, and in many species within the genera Poa, Stipa, and Festuca but not in Dactylis (cocksfoot) or Phalaris species.
Scientists have identified several toxins produced by endophytes; other unidentified toxins may also exist. The three main toxins in perennial ryegrass are lolitrem B, peramine and ergovaline. The levels of these toxins vary according to the strain of endophyte, the genotype of the host plant and the environment in which the plant grows. Drought and good plant nutrition, for example, favour production of toxin.
The species of endophyte found in perennial ryegrass, Neotyphodium lolii, has a seasonal growth cycle. In winter it makes little growth and is chiefly confined to the base of the plant. Growth accelerates in spring and early summer, which enables the fungus to grow within reproductive tillers, extending up toward the newly formed seed that then remain infected below the seed coat. The only means of further dispersal of the endophyte is by this infected seed. Endophyte within the seed can be killed by storage at high humidity over summer. Endophyte can be eliminated from plants by treating them with fungicide; this is not practical for a field situation. The concentration of toxin shows the same seasonal pattern as the fungus, although their distribution within the plant varies. Through most of the year, lolitrem and ergovaline are concentrated at the base of tillers.
Usually more than 70% of the fresh seed of perennial ryegrass sold in Australia is infected with endophyte. Consequently a high proportion of perennial ryegrass plants in pasture contain endophyte. Commercial quantities of ryegrass seed (of a limited number of cultivars) that are free of endophyte, have recently become available.
The endophyte gives infected plants an advantage over endophyte-free plants hence older stands of perennial ryegrass generally have higher proportions of the population infected.
In old Asutralian pastures about 90% of perennial ryegrass plants are infected with endophyte.
Effects of endophyte infection on perennial ryegrass host plants
- Enhanced resistance to some species of insect pests eg. African black beetle (Heteronychus arator) - but often the maturity of the insect affects their response. All three toxins, mentioned above, contribute to these effects. Improved resistance to some grass diseases including root rot, nematodes and virus diseases.
- Improved seedling vigour and hence better seedling establishment.
- Better photosynthesis under stress: An increased number of tillers are grown s when moisture or nutrients are limiting.
- Better drought tolerance.
- Increased seed production.
Our experience of these effects is limited. They depend on the genotype of grass, the strain of endophyte and the conditions under which the plants are grown. The extra vigour of the ryegrass plants, and possibly chemicals produced by the grass/endophyte combination, may reduce the productivity of companion legumes in mixed swards.
Effects on animals
Sheep, cattle, horses, deer, buffalo, antelope and alpacas can develop perennial ryegrass staggers when grazed on perennial ryegrass in autumn. Methods of avoiding staggers are discussed in the Agriculture Note Perennial ryegrass staggers and ill-thrift. On endophyte-infected perennial ryegrass, the rectal temperature and respiration rate of livestock is raised relative to stock on uninfected perennial ryegrass – particularly in the warmer months. Dags and flystrike problems in sheep are more common on endophyte-infected perennial ryegrass. Reduced lamb survival and a reduced growth rate of young sheep grazing endophytic ryegrass have been observed when comparisons have been made with similar sheep on adjacent endophyte-free ryegrass.
Experiments in South Australia, New Zealand and Chile have shown yields of milk, milk fat and protein, were lower when dairy cows grazed endophyte infected ryegrass compared with endophyte-free ryegrass. These are usually sub-clinical effects. That is, toxin concentration may be low and no clinical staggers symptoms are observed.
For more detailed information on the effects on animals refer to the Agriculture Note: Toxins in perennial ryegrass.
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